Suplatast tosilate [(±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]ethyl]dimethylsulfonium p-toluenesulfonate] exhibits excellent IgE antibody production suppressing effect, and is a useful therapeutic agent for various allergic diseases (Patent Document 1). As has been known, crystal forms of suplatast tosilate include a crystal form obtained through the method described in Patent Document 1 (hereinafter the crystal form may be referred to as the “first crystal form”); a crystal form described in Patent Document 2 (hereinafter the crystal form may be referred to as the “second crystal form”); a crystal form described in Patent Document 3 (hereinafter the crystal form may be referred to as the “third crystal form”); four crystalline polymorphs; and two solvates (Non-Patent Document 1).
As has been known, anhydrate crystals and hydrate crystals of the same compound exhibits different stabilities, although they have the same crystal form. In evaluation of evenness and stability of such crystals, the ratio between these two types of crystals can be estimated through differential scanning calorimetry or powder X-ray diffractometry, or the degree of stability of these crystals can be determined through measurement of water content. In the case of crystals of poor evenness (e.g., crystals containing amorphous substances), stability of the crystals, which is known to vary with the amount of such amorphous substances contained therein, can be determined through measurement of crystallinity of the crystals. However, with the exception of suplatast tosilate crystals of the first crystal form, there have not yet been reported crystals which are suggested, through measurement data, not to contain, for example, amorphous or other crystalline substances and water, which exhibit the same powder X-ray diffraction pattern, but which exhibit different stabilities. Therefore, needless to say, a method for determining such crystals has not yet been known.    Patent Document 1: Japanese Patent Publication (kokoku) No. 1991-70698    Patent Document 2: JP-A-1995-252213    Patent Document 3: WO 02/083633 pamphlet    Non-Patent Document 1: Proceedings of the 122nd Annual Meeting of The Pharmaceutical Society of Japan, 3, p 7, 26 [P] II-193, 194, 195    Non-Patent Document 2: J. Am. Chem. Soc., 124, 13139-13153 (2002)    Non-Patent Document 3: Angew. Chem. Int. Ed. Engl., 35, 2372-2374 (1996)